This is an open-label, prospective, observational, multicenter, randomized study to compare the efficacy between unrelated umbilical cord blood transplantation (UCBT) and HLA-haploidentical related hematopoietic stem cell transplantation ,after myeloablative conditioning for adult patients with hematologic malignancies.

Inclusion Criteria:

1. Age: subjects ≥ 18 and ≤ 55 years old.
2. Patients without suitable matched related donor
3. Diagnosed with acute leukemia or myelodysplastic syndrome in which allogeneic transplantation is considered the most potentially curative therapeutic option.
4. Written consent form signed.

Exclusion Criteria:

• Performance status: Eastern Cooperative Oncology Group(ECOG) score >2
• Prior allogenic hematopoietic stem cell transplant
• Left-ventricular ejection fraction at rest < 45%, uncontrolled arrhythmias or symptomatic heart failure.
• Diffusing capacity (DLCO) and/or forced vital capacity (FVC) < 39% of predicted values or symptomatic pulmonary disease
• Altered liver function tests (total bilirubin > 2 mg/dL and/or alanine aminotransferase, aspartate aminotransferase , and or active hepatitis or cirrhosis.
• Serum creatinine > 2 mg/dL or estimated creatinine clearance < 50 mL/min
• Evidence of uncontrolled bacterial, viral or fungal infection prior to the conditioning regimen
• Serious diseases that prevent patients from receiving chemotherapy treatments.
• Concomitant neoplasms.
• Pregnancy or breast-feeding.
• Any other medical, surgical or psychiatric condition that is considered by the attending and/or medical team as a contraindication for intensive treatment

Diagnosed with acute leukemia or myelodysplastic syndrome in which allogeneic transplantation is considered the most potentially curative therapeutic option